Aerosol containers have long presented a risk of explosion if over-pressures occur in the containers. Such explosions may occur when the container is subjected to high temperatures, e.g. when it is left in a very hot place, or when it is being disposed of or recycled.
If an explosion occurs when the container is left in a hot location such as an unattended automobile, this can cause considerable property damage. If an explosion occurs when the container is being incinerated, this can cause personal injury. For this reason, before aerosol containers are melted to reuse their metal, they are usually punctured. However, the spikes in the puncturing machines can miss a container, and if a pressurized container explodes in the molten metal in a furnace, the risk of injury and damage is particularly severe.
For the above and other reasons, various attempts have been made to provide pressure relief devices for aerosol containers. Typical such attempts are shown in U.S. Pat. No. 3,405,838 issued Oct. 15, 1968 to Preisendanz, U.S. Pat. No. 3,815,534 issued Jun. 11, 1974 to Kneusel, and U.S. Pat. No. 3,913,614 issued Oct. 21, 1975 to Speck.
The above identified attempts to provide aerosol container pressure relief devices have not in general been particularly successful. Their disadvantages include complexity, high cost of implementation, and difficulty in providing a narrow, precise range of pressures in which the relief device will vent.
The pressure relief device shown in the Kneusel patent has been used in some commercial aerosol containers. In this device, a pattern of lines is scored on the bottom of the aerosol container. The lines intersect at a common point to form a spoke-like design. The score lines weaken the bottom of the container, and the depth and number of lines determine the pressure at which the bottom will rupture. This arrangement obviously requires precise manufacturing operations to score the bottom of each container. Such operations are costly, difficult to perform, and are subject to imperfections which can affect the pressure at which the bottom of the container will rupture.
Recent developments have provided aerosol propellants that are considered more environmentally safe than previously, one such propellent being known as Propellent-22. While this propellent is preferable environmentally, it operates at a higher pressure than previous conventional propellants and has a steeper pressure/temperature curve (i.e. its pressure increases more steeply with temperature). This creates an increased risk of explosion unless a suitable pressure relief device is used.
Accordingly, it is an object of the present invention to provide a pressure relief device that is simple, inexpensive to manufacture, and which can be installed relatively easily and inexpensively in aerosol and other pressurized containers. The device of the invention may be designed to provide accurate pressure relief at a desired pressure range.